Steps to reproduce / testcase welcome (pasting the query and the error results)

Ok, this is stupid, but here you go:
https://de.wiktionary.org/w/api.php?action=review&revid=4021885&token=redacted&flag_accuracy=1
{"servedby":"mw1204","error":{"code":"missingflag","info":"'flag_accuracy' parameter missing from query.","*":"See https://de.wiktionary.org/w/api.php for API usage"}}

https://de.wiktionary.org/w/api.php?action=help&modules=review doesn't even know a "flag_accuracy" parameter, only in the example.

Evidently caused by 4cf8187fe6bac0b089c70612ef4ab4d3179d99cd. @Chad, could you have a look at this?

My guess is that if ( !FlaggedRevs::binaryFlagging() ) should have been put around that code, but it's only a guess.

Maybe? I really was grasping at straws with that patch as it was unclear why the error was occurring to begin with.

Now causing issues on enwiki with Twinkle, see WT:TW. Any chance of reverting that patch until a fix can be found?

In T86258#972570, @TTO wrote:

Now causing issues on enwiki with Twinkle, see WT:TW. Any chance of reverting that patch until a fix can be found?

Link is https://en.wikipedia.org/wiki/Wikipedia_talk:Twinkle#Issue.3F and says:

When reviewing pending changes and reverting I sometimes get "Automatically accepting your changes: 'flag_status' parameter missing from query.",

Change 184916 had a related patch set uploaded (by Anomie):
API: Fix action=review for binary flagging

https://gerrit.wikimedia.org/r/184916

Patch-For-Review

Change 184916 merged by jenkins-bot:
API: Fix action=review for binary flagging

https://gerrit.wikimedia.org/r/184916

Change 185180 had a related patch set uploaded (by Anomie):
API: Fix action=review for binary flagging

https://gerrit.wikimedia.org/r/185180

Patch-For-Review

Change 185180 merged by jenkins-bot:
API: Fix action=review for binary flagging

https://gerrit.wikimedia.org/r/185180

This should be fixed on all WMF wikis now.